Credit: Hacker's Delight, Section 2-1: Manipulating Rightmost Bits
Use the following formula to create a word with 0’s at the positions of the trailing 1’s in the input, and 1’s elsewhere, producing all 1’s if none (e.g., 10100111 -> 11111000)
`default_nettype none
module Bitmask_Turn_Off_Trailing_1_Bits
#(
parameter WORD_WIDTH = 0
)
(
input wire [WORD_WIDTH-1:0] word_in,
output reg [WORD_WIDTH-1:0] word_out
);
initial begin
word_out = {WORD_WIDTH{1'b0}};
end
localparam ONE = {{WORD_WIDTH-1{1'b0}},1'b1};
always @(*) begin
word_out = ~word_in | (word_in + ONE);
end
endmodule